Carbonization of coal



June 18, 1963 w, KRUPPA 3,094,467

CARBONIZATION OF COAL Filed July so, 1954 2 Sheets-Sheet 1 Ha /A I N VENTOR.

BY W/u/AM .I fT/PUPPA June 18, 1963 w. J. KRUPPA 3,094,467

CARBONIZATION 0F com.

Filed July so, 1954 Y 2 Sheets-Sheet 2 I N VEN TO MAL/AM f fizz/PR4United States Patent a" 3,tl 4,467 CARBONIZATION OF COAL William J.Kruppa, Somerville, N.J., assignor to American Cyanamid Company, NewYork, N.Y., a corporation of Maine Filed July 30, 1954, Ser. No. 446,83211 Claims. (Cl. 20222) This invention relates to the carbonization ofcoal, more particularly to a method of producing high grademetallurgical coke while concomitantly producing high yields of valuableliquid products.

The metallurgical coke employed in industry is largely produced inby-product coke ovens; but a minor amount is produced in beehive ovens.As is known, in the byproduct oven, the coke is produced by the hightemperature distillation of selected grades of bituminous coal in aclosed retort Without access to air. The primary product of such anoperation is metallurgical coke and the charge material is selected andthe operating conditions adjusted so as to produce a hard, porous cokesuitable for the reduction of iron ore in a blast furnace. Theco-products of the operation are coal tar, coal gas and ammonia. Thedesideratum in such operations is a high quality coke and this resultsin a relatively low yield of liquid products and a high yield of gas.Because of the high temperatures employed, necessitated by the indirectheating utilized and to the physical structure of the ovens, theoriginally evolved, volatile materials are subjected to excessivepyrolysis and hence the ultimate liquid products produced are comprisedlargely of heavy, residual products of a tarry nature.

The physical structure of the byproduct coke oven and the nature of theoperation impose certain restrictions on the charge material, that is tosay, to selected grades of coal that do not unduly swell or cake. Thereare many grades of bituminous coals that swell and cake badly but whichare otherwise suitable for the production of metallurgical coke andother products such as partially coked briquettes.

The present invention relates to an improved method of producing anexcellent grade of metallurgical coke from bituminous coal and is ofparticular economic value because it may utilize a wide range ofbituminous and particularly badly swelling and caking coals which cannotbe utilized in a byproduct coke oven.

In order to more clearly explain the invention, a preferred embodimentof a process unit will be described and is illustrated in theaccompanying drawings in which:

FIG. 1A is a view, partially in elevation and partially in verticalsection, of the coal preconditioning unit.

FIG. 1B is a similar view of the connected units in which thepreconditioned coal is briquetted and carbonized.

The process of the invention, as will be seen more fully hereinafter,combines the advantages of the high temperature by-product cokingprocess and the low-temperature carbonation method in that, like theby-product oven operation, it produces an excellent grade ofmetallurgical coke and as in the earlier low-temperature carbonizatio-noperation, it insures a large yield of primary tars. It also producesappreciable amounts of gas of substantial fuel value. The novel processof the invention is designed to economically process a wide range ofbituminous coal, operating efficiently on grades from those havingslight coking properties to those characterized as badly swelling andcaking coals.

Considered generally, the process comprises a special preconditioning ofthe coal in finely divided form to modify its caking and swellingproperties and to improve the coal in other particulars; briquetting orextruding the 3,094,467. Patented June 18, 1963 'ice coal with animproved binder derived from a coproduct of the process and distillingand carbonizing the briquettes by direct contact with a stream of hotrecycle gas from which the originally evolved condensables have beenremoved.

It has long been known that weathering reduces the swelling power ofbituminous coals and such reduction could be achieved by acceleratedoxidation employing heated oxygen containing gas or other oxidizingagents. The oxidation methods proposed heretofore, generally considered,contemplated a treatment at relatively low temperature for prolongedperiods of time as, for example, at a temperature of around 150 C. for aperiod of from 24 hours to hours or more, depending on the type of coalprocessed. Such earlier treatments presented many disadvantages includedin which was the excessive storage capacity required for treatment andthe batch nature of the operation. The prior art discloses manysuggestions as to methods of shortening the oxidation treatment such as,carrying out the oxidation under superatrnospheric pressures of theorder of 50 to 15 0 p.s.i. and temperatures of the order of from aboutC. to 200 C. or by subjecting heated coal alternately to pressure andvacuum. Such methods, however, still entail a relatively prolongedtreating period of several hours and are essentially batch operationsrequiring retention periods in expensive pressure tight containers ofsubstantial capacity.

The present process invokes and utilizes a novel coal preconditioningtreatment. It is found that when this is properly correlated with properbriquetting or extrusion techniques, an improved carbonization of a widepermissive range of charge material may be effected to produce asuperior grade of metallurgical coke and a high yield of valuableco-products.

The method of preconditioning the coal is based on the concept ofoxidizing the coal at high temperatures, but for a very brief intervalof time, followed by immediate, rapid cooling of the heated coal to stopthe oxidation. This preconditioning essentially is a continuous flashoxidation conducted on particulated coal fluidized in the oxidizinggaseous medium which conveniently is ordinary air, followed by a flashcooling of the oxidized coa As will be more fully appreciated from aconsideration of the subsequent disclosure, the novelty of the presentinvention is the more arresting because the basic procedure iscontra-indicated in the prior art. As Will be explained more in detail,the oxidation is carried out in the presence of an oxygen-containingatmosphere such as air and the coal is heated in the presence of suchoxygen-containing gas to temperatures to and above the threshholdignition temperature. In these circumstances complete combustion of thecoal, rather than controlled oxidation, would be expectable. However, aswill be more fully elucidated, this high temperature oxidation iscarried out under such conditions of high thruput ve locity and rapidquenching that the retention or dwell period at the high temperatures isexceedingly brief, and of the order of 10 seconds, more or less, so thatactual ignition does not ensue. Another characteristically novel factoror condition in the process is that the particulated coal is suspendedin high concentration in an air stream and is heated in the so-calledplastic range so that the actual oxidation of the coal is largelyeffected while the coal is in a special physical condition or state,namely as a viscous plastic or quasi-liquid particles dispersed in agaseous magma. Such a procedure, per se, i.e., heating powdered coal tothe viscous or plastic range, would be expected to, and normally would,result in the agglomeration of the plasticized coal particles intolarger cake-like bodies. However, in the novel procedure, this hightemperature treatment is carried out on the solid or plasticizedparticles of coal which move at a very high veolcity in a constrictedpath of confined cross-section and while maintained in a constrictedpath are shock cooled or rapidly quenched from the platsic to the solidphase. In these circumstances but very little agglomeration of the coalparticles occur as the mesh size of the oxidized quenched coal particlesis only slightly above that of the charge stock. This retention of thedesired particle size is due, among other things, to the fact that thecoal particles, whether in solid or semi-fused form, constitute adispersed phase in a high velocity air stream; to the low retentionperiod which the coal is in the plastic state and probably to someconsiderable degree to the mutual attrition of the resolidified coalparticles which occurs in the rapidly moving fluid stream.

This method of preconditioning has many advantages and, as will be seen,lends itself ideally to the continuous production of metallurgical coke.Inasmuch as the thermal preconditioning treatment is but for a verybrief period of time and the retention period of the coal in the heatingapparatus is extremely short, a very large thruput is achieved in arelatively small oxidizing unit. This method of flash oxidation in theplastic range of the coal and quick cooling thus eliminates thenecessity for the large and costly pressure equipment required byearlier proposed methods.

This coal preconditioning treatment insures many other advantages whichare of peculiar and special import with respect to the character of thecoke ultimately produced. The flash oxidation not only reduces theswelling and caking properties, but also, with most types of coal,unexpectedly lowers the sulfur content of the coke pro duced from theoxidized coal. This is of very considerable significance in theproduction of metallurgical coke because, as is known, the presence ofsulfur in the coke is detrimental, especially when the coke is used inblast furnace reductions. In such blast furnace operations, it costsapproximately about twenty-five cents to remove each tenth of a percentof sulfur, this cost being represented by the extra coke and limestonerequired.

Another advantage of the flash oxidation method is its effect on the ashcontent of the ultimately produced coke of the treated coal. When suchpreconditioned coal is employed in the present invention, the finishedcoke shows a lower ash content than a coke produced from coal which isnot subjected to such preconditioning treatment. Another factor of notinconsiderable significance, is that the softening temperature of theash in the flash oxidized coal is substantially higher than the ash ofthe same coal which is unoxidized, for example, it was determined thatthe softening temperature of the ash of a sample of raw Heisley coal was2320 F. whereas this same type of coal which was subjected to flashoxidation was found to have the softening temperature of the ash at 2570F. The reason for this reduction in the ash content as effected by theflash oxidation is obscure, and difficult to precisely explain. It maybe due to a physical separation of some of the ash forming constituentsas a result of a winnowing eifect taking place in the turbulant streamof the triturated coal or possibly to :a chemical conversion ofmetaliferous components to a more evolvable form. Whatever may be themechanism of reaction, the described beneficial reduction in ash isaccomplished by the flash oxidation.

There is another inexplicable action which takes place during or becauseof the flash oxidation, and that is the reduction of the criticalcharacter of the rate of heat input during the so-called critical rangein the heating of the briquettes or extrusions in the carbonizingretort. This critical range may be defined as the temperature rangeextending from approximately 350 C. to about 500 C. in which softeningor fusion of the coal takes place and in which upon evolution ofvolatile material the coal mass resolidifies. In the past it was thoughtthat the rate of heat input to the coal compacts in this range had to becarefully controlled and the limit of safety was of the order of about2.5 C. per minute; if the rate of temperature rise, in this range,materially exceeded this rate, briquettes, for example, tended todistort and adhere to each other and in addition suffer a loss in headload strength. This critical effect was found, in the past, to besomewhat reduced by forming briquettes of pulverized coal of minus 20mesh. It was discovered that when the coal from which the briquette orextrusion was formed was first subjected to the novel flash oxidation,this critical effect was mitigated to a surprising degree, so much so,in fact, that the critical character of the range does not obtain to thesame extent when carbonizing the flash oxidized coal. Operations havebeen carried out, in the manner to be more fully described hereinafter,in which briquetted or extruded flash oxidized coal has been carbonizedand in which the rate of heat input within the range 350 C. to 500 C.was of the order of up to 5 C. per minute. This, as will be appreciated,is most important, because in earlier operations the slow rate of heatinput during the plastic or critical range was a limiting factor on thethruput of coal preforms in the retort. There is thus an intimate andunobvious correlation between the type of flash high temperaturepreconditioning of particulated coal and the retort operation which wasunappreciated and unutilized heretofore.

I-n carrying out the process, the bituminous coal or blends or mixturesof selected grades of coal are dried and pulverized prior to theoxidizing treatment. It has been ascertained that the presence of watervapor in the oxidizing gas tends to somewhat retard the oxidation of thecoal. It is thus desirable to dry the coal particles to less than onepercent free moisture.

The particle size of the coal to be treated, while not critical is quiteimportant. It has been found that improved results are assured bypulvenizing the coal so that 100 percent is minus 20 mesh and at leastpercent is minus 28 mesh. Controlling the mesh size is quite importantsince it has a direct bearing on the flash oxidation treatment and onthe physical character and thermal behavior of the subsequently formedbriquettes. If the coral particles are too large, it is more difficultto achieve uniform oxidation and the time required for satisfactoryoxidation is prolonged, furthermore, the large coal particles result ina sandy texture of the raw briquette or other preform and a reduction inabrasive strength of the briquette.

In operating the process, the coal or blends of coal to be treated arecontinuously taken from a suitable storage bin (not shown) and fedthrough the conduit 1 to any suitable unit in which the coal isparticulated and dried to the desired degree. This obviously may be donein dilferent specific manners utilizing any suit-able apparatus. Thusthe coal may be ground to a particle size suitable for drying, using anysuitable type :of mill such as a ham Iner mill, dried in an economicaldryer such as a rotary kiln dryer and then passed to an air sweptpulverizi-ng mill. In the illustrative embodiment the coal is pulverized:and dried contemporaneously. The coal passes from the conduit 1 to asuitable mill such as the roller mill 2. In lieu of the roller mill, anyother effective triturating apparatus may be employed.

In the embodiment depicted in the drawing, the coal which is pulverizedin the mill 2 is picked up in a stream of a hot drying medium such ashot gas admitted from the furnace 3 through the conduit 4, the flow ofwhich is controlled by damper 4'. The furnace 3 may be of any desiredtype but in the preferred embodiment, i.e., one in which coal iscontinuously preconditioned, briquetted or extruded and carbonized, thefurnace conveniently is a gas fired type the fuel for which is fuel gasderived in the carbonization treatment which, as shown, may be fed tothe furnace in cont-rolled amounts through the gas feed line 5. Thisline preferably is provided with a flow meter and thermostaticallycontrolled feed valve so as to establish and maintain the temperature ofthe exit gases at the desired value.

The pulverizer, as shown, is connected in a classifier circuit whichincludes the discharge conduit 6, a solids separator such as the cyclone7, the fluid recycle conduit 8, circulating fan 9 and the return conduitr10 which discharges back into the mill 2. The operation of this airswept mill is apparent. When the unit is on stream, the fine coalparticles formed in the mill, i.e., those less than about 20 mesh, areentrained in the stream of hot gas entering from the furnace and areforced by circulating fan 9 through the discharge conduit 6 to thecyclone 7. The larger coal particles drop out of the circulating streamand are further reduced in the mill. In the cyclone 7 most of thesuspended coal particles are separated and the hot gas largely freed ofparticulated coal is returned to the circuit through line 8.

As shown, the pulverizing-drying unit also includes a vent circuit. Thisincludes line 11 controlled by valve 11, having the interposed motordrive vent fan 12 which line connects at one end with recirculatingconduit 10 and at the other with a fluids-solids separator such as thecyclone 13. The solids separated out in cyclone 13 are returned to themill through a suitable return line 14 and the solids-denuded gas isvented from the system through vent line .15. During operation thepositively driven vent fan 12 removes heated gas from the mainrecirculating circuit, in amounts controlled by valve 11' and dischargesthis gas into the cyclone v12$. Herein the entrained coal particles areseparated and returned to the mill and the waste gas is dischargedthrough vent 15 to atmosphere. As will be appreciated during theoperation, the vent circuit is controlled so as to discharge or ventfrom the system a quantity of gas equal to that admitted from thefurnace 3 in addition to the water vapor evolved from surface moistureand some water of constitution in the coal.

The above described pulverizing and drying unit produces a suitablypulverized dried coal adapted for the improved preconditioningtreatment. As explained previously, such pulverized dried coal may beprepared in any other suitable manner. The hot dried coal which collectsin the low sections of the cyclone 7 is fed through the discharge line16 to a unit in which the coal is fluidized prior to the flashoxidation. The coal removed from the cyclone 7 is discharged throughline 16 into an accumulator or feed tank 17 which in turn feeds the coalto my suitable fluidizing unit. This feed tank 17 is desirably providedwith suitable level indicators 13 and with a pressure indicator (notshown). The tank also preferably is provided with manually controlledvalved draw off line 19 from which coal may be withdrawn for currenttests and checks.

The coal may be fluidized in any suitable type of fluidizing unit. Inthe descriptive embodiment the unit is illustrated as a conventional:Fuller-Kinyon pump. In the continuous operation coal is fed from thefeed tank through any suitable pressure retentive valve such as therotary vane valve 20 to the fl-uidiz-ing pump 21. This coal istransported by a continuous screw to the discharge side of the pump andin transit is aerated and fluidized by air forced into the pump from thecompressor 22 through the line 23. The [air feed to the compressor ispreferably filtered in filter 24. The fluidized coal, as shown, isdischarged from the pump into transfer line which is connected to theflash oxidizing zone. As will be understood, the pump inlet line 23 anddischarge line 25 are preferably provided with suitable pressureindicators.

It has been found during test operations of the process that thequantity of air required for adequate aeration and fluidizing of thecoal may vary somewhat. Effective oxidizing has been obtained using aratio of substantially 8 lbs. of coal per pound of air, however, higherratios of the order of about 12 to 15 lbs. of coal per pound of air maydesirably be employed.

In the preferred oxidation treatment, the fluidized coal is passed in acontinuous stream through an elongated confined passageway and israpidly heated to a high temperature in one portion of the passagewayand is then immediately quickly cooled or quenched in an adjoiningportion of the passageway.

As shown in the drawing, the flash oxidation and flash cooling can mostconveniently be effected by passing the fluidized coal through acontinuous coil. The fluidized coal, passing from the pump 21, is forcedthrough transfer line 25 into the heating coil 26 and thence through theconnected cooling coil 27. The heating section of the coil, as shown,may be located in a suitable furnace 28 and desirably in the combustionzone so as to insure rapid transfer of heat to the coal stream;preferably the stream of fluidized coal passes through the furnace in adirection countercurrent to the flow of combustion gases. As will beunderstood, the furnace 28 may be of any desired type and convenientlymay be a gas fired furnace the fuel for the burner 29 of which is fuelgas derived from the subsequent carbonization operation and fed throughline 5'. As this line 5' previously described is provided with asuitable flow meter and temperature recorder so that the operation maybe effectively, currently checked.

The flue gas from the furnace passes out through stack 39 under a draftcreated by steam or water injected into the stack throughvalve-controlled line 31.

The heated fluidized stream passes immediately and continuously from thecoil 26 to the quench coil 27. Preferably the fluidized stream, asshown, passes upwardly in coil 27 and during such passage is quicklycooled in any suitable manner as by means of a spray of water or othercoolant fed through the line 32 and spray head 33, immersion in a tankof a coolant or by any other effective means.

When the spray cooling technique is employed, the used cooling Water maybe collected in the tank 34 from which it may be withdrawn through line35.

The cooled fluidized stream of oxidized coal passes continuously fromthe coil 27 through the transfer line 36 to a fluid-solids separatorsuch as the cyclone 37 in which the oxidized coal particles areseparated from the entraining gas and water vapor which latter arevented to atmosphere through the stack. The cooled oxidized coalparticles accumulating in the cyclone 37 may be drawn off through theline 39 (FIG. 1B) and passed directly to the briquetting or extrusionunit of the plant or, when required, all or a portion of the coal may bedirected through line 40 to storage from which it may later be withdrawnfor the fabrication of briquettes or extrusions. The cyclone preferablyis provided with the sample draw off line from which samples may besecured for periodic check tests.

The improved preconditioning of coal, as effectuated in the describedapparatus can be more readily appreciated and evaluated from aconsideration of a typical operation. A large number of runs have beencarried out in a unit such as that described, having a thruput capacity,through the oxidizing zone, of 13 tons per hour. In this unit theoxidizer coal 26 consisted of 600 linear feet of 6 inch diameter alloysteel pipe and the connected cooling coal 27 was of the same size andlength. In the usual operation when the unit is on stream, thetemperature of the drying air passing through the furnace 3 to thepulverizer is controlled at about 500 'F. The furnace Z8 is operated soas to raise the temperature of the fluidized coal stream to betweenabout 675 F. and about 800 F. and desirably between 700 F. and 750 F.The pressure on the fluidized stream at the exit of pump 21 may bebetween about 20 and 25 lbs. per sq. in. In such circumstances theactual velocity of the coal stream at the exit of the fluidizer pumpranges from about aorta is? 1200 to 2000 or more ft. per min. With suchvelocity in an oxidizer coil of the dimensions given, theretentionperiod of the coal is only about 10 to 15 seconds. As

will be appreciated during passage through the oxidizer and coolingcoils the pressure progressively diminishes and isreduced tosubstantially zero pressure at the cooler. The cooler is operated so asto very rapidly reduce the temperature down to the lowest convenientvalue to check the oxidation reaction and to cool the coal to a degreesufficient to insure convenient subsequent handling. The fluid stream,passing through the cooler coil, as will be understood, contains watervapor evolved from Water of constitution and partial decomposition ofthe coal.

The rapid chilling or cooling of the oxidized particulated coal, aspreviously pointed out, is a very important feature of the invention. Ifthe par-ticulated coal which is highly heated in coil 26 is not cooledquickly, over oxidation of the coal would result thus negating theadvantages of the treatment. In the treatment described, the amount ofoxidation is controlled within selected narrow limits. Thus in thespecific example an analysis of the exit air (from cyclone 37) shows anoxygen content of 16% so that but approximately of oxygen in the aircarrier stream is utilized in the controlled oxidation.

It will be understood that the requirements that the particulated coalbe flash heated and flash cooled in a brief period of time imposes somelimitations on the diameter of the coil, i.e., the cross-sectional areaof the air-coal mass to be heated and cooled. It has been found that foreffective commercial operations the heating and cooling coils should notbe materially below two inches and not substantially more than sixinches internal diameter.

It will have been appreciated that the improved method ofpreconditioning bituminous coal to alter its swelling and cakingproperties essentially involves extremely rapid or flash oxidation in agas stream of substantial oxygen content at elevated temperatures at orabove the threshhold ignition temperature of the coal and at or abovethe plastic range of the particulated coal. This flash heating andoxidation'is instantaneously followed by a flash or shock chilling ofthe confined stream of dispersed particulated coal to abruptly check orinhibit further oxidation. The apparatus shown in the drawings isdesigned and has been found to operate effectively to achieve thedesired results. It is apparent, however, that other and specificallydifferent designs and types of apparatus of a functionally equivalentnature may be utilized in effectuating the process. Thus while theillustrative embodiment involves a particular pulverizing and dryingcircuit in which the coal is pulverized in an atmosphere of drying gas,it is apparent that the same results may be achieved by specificallydifferent methods employing apparatus other than that shown herein. Thusthe raw coal may be preliminarily crushed in any suitable crushingapparatus, dried in any suitable drying unit, such as a rotary kilndryer, and then fed to the pulverizing mill which may or may not be airswept. Other apparatus and methods for producing a dried, suitablyparticulated coal are within the compass of the invention.

In the course of study and investigation of the effects of the describedflash oxidation treatment on different types of bituminous coals andvarious blends of such coals, it was ascertained that, with some rareexceptions, coke which is made from compacted units of particulated coaloxidized by the described procedure and carbonized as hereinafterdescribed displayed a significantly lower sulfur content than cokeproduced from the same coal which was not preoxidized. It was similarlyascertained that coke made from the oxidized coal, in all cases, showedless ash content than coke made by the same procedure from the same coalwhich was not preliminarily oxidized.

The above mentioned reduction in the sulfur and ash content of the cokeproduced from oxidized coal is shown in the following table. The resultsrecordedvare from runs in a semi-commercial unit in which coa-l blendswere flash oxidized and flash cooled in accordance with the describedprocedure and the oxidized coal was briquetted using a sulfuricacid-treated tar binder, in accordance with US. Patent 2,314,641 usingapproximately 11% of binder on the coal. The briquettes were carbonizedin a vertical retort under the conditions prescribed in the US. Patentto Berry 2,131,702. The results recorded in Table I represent theanalysis of composite samples of a one day run and a five day run.

TABLE I Typical Analyses of Solid Materials COMPOSITE SAMPLES OF ONEDAYS RUNFIN. TEMP. COKE 830 C.

Pulv Raw Coal Oxid. Raw Coke Coal Grab Coal Briqt Sample Vol. Matter(Dry) 18. 39 18.13 17. 67 24. 39 0.75 Fixed Carbon 74. 75. 57 77. 05 69.92 91. 97 6. 76 6. 10 5. 28 5. 69 7. 28 Sulfur 1. 4O 1. 23 0.95 1. 31 1.04

COMPOSITES-FIVE DAYS RUN Vol. Matter (Dry) 18.41 18.02 17.50 24.12 0.89Fixed Carbon- 74. 75 74. 68 77.02 70. 46 92.85 Ash 6. 84 7. 30 5. 48 5.42 6. 86 suirurm. 1.58 17 65 1.26 1. 53 1. 03

The raw briquettes designated in the table contained 11% tar pitchbinder which contained approximately 10% of sulfuric acid.

A study of the data recorded in the above table reveals the strikingeffects of the flash oxidation treatment on the ash and sulfur contentof the oxidized coal and finished coke. The ash and sulfur content ofthe oxidized coal is significantly lower than that of the raw coal andgrab samples. Notable, too, is the fact that the softening temperatureof the ash in the oxidized coal is measurably higher than that of theraw coal.

The particulated coal processed as above described by flash hightemperature oxidation and flash or shock cool ing may be formed intounits of the desired shape and size, by any suitable procedure such asbriquetting or extrusion, and may be then carbonized in a continuousretort to a metallurgical grade coke. Since the optimum conditions forbriquetn'ng the particulated coal and extruding preforms of such coalvary somewhat, these procedures will be separately described.

In one procedure under the invention, the oxidized particulated coal iswithdrawn from line 39 (or fromstorage) and passed to a mixing unitwhere the coal is thoroughly mixed with a hot binder and is passed tothe briquetting machine 43 of any standard or conventional type. Onetype of binder which has been found to be efiective comprises a heavytar or pitch fraction derived wholly or in part from a subsequentdistillation of products evolved during the carbonization of the coaland charged to the binder make-up tanks 44 and 47. This binder may bechemically modified by the addition of from about 8% to about 15% ofsulfuric acid admitted through lines 46. The acid is thoroughly [mixedwith the binder by suitable agitating paddles, as shown, and retained atthe desired elevated temperature by control of steam through the steamcoil 45. The pre-mixed binder is passed from mixer 44 to the heatedbinder supply tank 47 from whence it is withdrawn, in the desiredamount, through line 48 and is discharged to the mixer 42.

The hot fluent binder is thoroughly mixed with the particulated coal inmixer 42 in' amounts sufiicient to produce briquettes of the desiredcharacteristics of high raw and cok-ed strength and good abrasiveresistance. In

usual circumstances, from to 10% of this binder is employed in thebriquetted coal mixture. If desired, a corrosion inhibitor, such aspotassium dichromate, may be added to the binder to inhibit acidcorrosion of the briquetting rolls. While such an acid treated binderdoes serve etfectively, it does have the disadvantage of requiring themixing of acid and does present a corrosion problem. The preferredbinder, to be described subsequently, comprises an acid-free pitchproduct which may be derived wholly or in part from distillationproducts of carbonization.

The binder-coal mix, as noted, is passed to the briquetting rolls andbriquettes are discharged from this press usually at a temperature offrom about 40 C. to 95 C. At this stage, the binder is relatively soft.The hot briquettes are then passed over a chute 4 8 provided with ascreen 49 to the conveyor 50. Fines passing through screen 49 arereturned by a conveyer 51 back tothe mixer 42. In passage along theconveyer, the warm briquettes are cooled with minimum tumbling ormovement down to a temperature of between about 30 C. to 40 C. at whichtemperature they are hard enough to withstand normal handling, i.e.,transportation by typical conveyors such as elevator conveyor 81 fordischarge into the carbonizing retort. Any excess of briquettes .abovethat required for a retort charge may be directed to temporary storage,as for example, by diversion through chute or passageway 52 to storagebin 53 from which they may be charged as required through gate valve 54and conduit 55 back to conveyor 50.

The briquettes which are to constitute a retort charge are fed bygravity through the line 55 controlled by valve 56 to the verticalretort 57.

In the carbonization operation, the briquettes pass by gravitycontinuously down the retort and during such passage are subjected todirect intimate contact with a countercurrently flowing stream ofnon-reactive gas wherein they are carbonized to a finishing temperatureof from about 850 C. to lO00 C. or more to produce tough, densecarbonized units of the desired low volatile content of the order of 1%to 2%. Such finishing temperature, as will be understood, is chosen inrelation to the desired reactivity and volatile content of the coke.

The heating gas stream in the retort is made up, in effect, of twomerged streams which are derived from the carbonization operation andwhich have been stripped of condensable components. One such gas streamis fed through line 58 to a combustion chamber 59 where it is heated bypartial combustion in the combustion chamber with air introduced throughline 60 by the action of blower 61 and after such partial combustionenters the tuyeres.

The second stream of gas comprises a quench gas which enters the loweror quench section of the retort through line 62 in controlledquantities. This gas directly contacts and abstracts heat from the hotcarbonized briquettes, being thereby preheated, and in passing upwardlyin the retort merges or mixes with gas entering through the tuyeres andthe merged streams pass upwardly in the retort. The exit gases pass outof the upper section of retort through the main 63 and are treated inany desired manner to remove the tar and to provide the desiredtar-denuded gas for recycling to the retort.

When bringing the retort up to temperature, preparatory to putting it onstream, the gas feed line 37 may be employed since for such preheatingoperation the volume and temperature of the tuyere gas is not important.

In this operation the heating of the briquettes or extrusions iseffected in a progressive manner, as they pass down the retort, bydirect contact with relatively large volumes of stripped recycle gas. Insuch passage the units are subjected to an increasing temperaturegradient during which passage condensable volatile material and fixedgases are evolved. In the operation of the process, the quantities ofgases fed through the lines 58 and 62 and the temperature of the tuyeregas are so correlated and controlled, that the volume of gas passingupwardly in the retort has a heat capacity which substantially balancesthat of the charge of briquettes or extrusions being heated. In thepassage down the retort the compacted units are subjected to increasingtemperatures in an atmosphere of hot gas which is characterized by avery low partial pressure of the volatile or evolvable components. Theheating is controlled at such a rate as to avoid distortion and crackingof the compacted coal units. 'In the lower sec tion of the retort, asshown, the compacted units are subjected to the desired high finishingtemperature of from 800 C. to 1000 C. and are thereafter quenched by thestream of quench gas and are discharged to conveyer 64 and conveyed tostorage. The upwardly flowing gas sweep out evolved tars and lightervapors into the upper section of the retort thus minimizing excessivepyrolysis or crack- :ing of such evolved products.

An additional or supplemental stream of hot product gas may beadvantageously utilized in the retort. This stream is fed to the uppersection of the retort through the line 35 after being preheated to atemperature of the order of from 200 C. to 400 C. The sensible heat ofthis gas stream is imparted to a substantial degree to the incoming coalunits, preheating such units and at the same time minimizing orinhibiting the condensation of tar from the tar-containing vapors; suchcondensation normally would occur if such vapors contacted coldbriquettes or extrusions. Such entering stream of flush gas enters theretort countercurrently to the main upwardly flowing merged gas streamand buffers or checks the flow of the latter into the top of the retortwhere condensation of tar might otherwise occur.

The vapor-laden gases pass through the main or downcommer 63 to anysuitable tar settler or knockout box 65. Preferably the efliuent streamof gas discharged from the retort is quickly cooled by any suitablecoolant, such as water, which is admitted to the efiluent stream throughthe line 67. This coolant, which can comprise a supernatant liquid layerfrom knockout box 65, may be continuously recirculated by withdrawing itfrom the box 65 and forcing it by pump 67' to the main 63. The make-upcgolant, in required amounts, is admitted through line 6 The liquid tarfraction, settling out in unit 65, is discharged through line 63 and isforced by pump 68' through line 69 and after suitable heating, forexample in heated still 76, a portion may be utilized for the binderrequirements for the binder-make-up by passing the desired frac tionfrom still 70 through line 71 to the binder make-up system.

The gas, from which the entrained tar has been scrubbed, is passed fromknockout box 65 through the main 72 and is treated by any suitable orconventional method as, for example, in the scrubbing tower 73 toseparate additional quantities of tar and to separate and condense thecondensable components. The gas separated in such operations andwithdrawn from tower 73 through line 75 is split into several streams toserve as a source of recycle gas for the carbonization operation and ifdesired for heating gas, passed through line 5 to the coal heatingfurnace. This recycle gas, when desired, may be supplemented by gasintroduced into the cycle from an extraneous source. The scrubbingliquid collecting in the base of tower 73 is withdrawn and passedthrough pump 76 and line 77 to the top of tower 74, where it isregenerated for reuse by contact with air introduced through line 78.

The carbonization retort employed may be of any suitable design andconstruction and of the desired capacity. The retort shown comprisesessentially a steel shell provided with a refractory lining, such afirebrick. The steel shell may be lagged on the exterior with suitableinsulating material. If desired, however, the retort may be of any otherdesired shape. In a typical case, a 200 ton a day production may becarried out in a spe rs-e7 round retort of substantially twelve feet indiameter and of the order of about thirty feet or more in height.

The product produced by the above described method of flash oxidation ofparticulated bituminous coal followed immediately by shock cooling,subsequent compaction of the oxidized coal into units of predeterminedsize and shape, and the controlled carbonization of these units in themanner described, results in coke-like products of eminent utility. Thecarbonized units are uniform in size and composition and are ofcontrolled density thus assuring uniform operation in use, as forexample, in a blast furnace or cupola operation. The size and shape ofthe fuel units readily can be controlled to insure the desired orrequisite permeability of the bed to the passage of gases therethrough.

In the preceding description, the novel operation of the invention wasdescribed, illustratively, with reference to the briquetting ofspecially preconditioned coal with a specific binder such as sulfuricacid-treated coal tar pitch. This described operation has been found tobe quite effective. However, the permissive scope of the inventionextends considerably beyond this particular operation. The specialpreconditioning of the coal has been found to so modify the coal that itis rendered amenable to bonding with other and specifically differentbinders and utilizing different techniques for compaction of the coal.

Continuing research on the problem of compacting oxidized coal particlesand preforming these into selfsustaining units of suflicient strength toundergo or withstand the cond-itions incident to carbonization haseventuated in certain novel findings of profound technological value. Aswill be explained more fully hereinafter, it has been found, among otherthings, that the head load strength of briquettes and extrusions may beconsiderably increased by the incorporation of certain water-solublebinders in the main binder pitch mix. It has also been ascertained thatwhile acid-treated binders operate effectively, the addition of acid isnot essential. It has been found that effective bonding of theparticulated coal may be achieved with acid-free coal tar or pitchbinders, provided certain conditions are established and maintained. Ithas further been determined that by proper control of binder-to-coalratios, water content and aqueous wettability of the coal particles,coal-binder mixes may be produced which are readily extrudable toproduce extruded units of excellent green strength and which can becarbonized, under the general conditions previously described, toproduce strong, tough coked units of predetermined shape and controlleddensity which perform excellently as metallurgical coke in reductionoperations involving the use of such coke.

One of the important factors in the successful operation of the processis the development of adequate headload strength in the briquettes orother preformed units. It has been found that the headload strength ofpreforms of compacted oxidized coal is somewhat limited. Such headloadstrength may be increased by invoking a number of expedients. Evidence,adduced in operation of the process, indicates that the failure ofbriquettes or other preforms, under headload, apparently is due, amongother things, to the fact that because of the general homogeneity of thestructure of the briquette lines of cleavage tend to develop in theunits which cleavage lines or planes induce or facilitate fracture ofthe units. It has been determined that this tendency can besubstantially minimized by in corporating in the coals-binder premix aheterogeneous and preferably a substantially inert solid phase. Thisapparently serves as an aggregate which imparts considerable strength tothe compacted unit. Such an additive or aggregate may comprise, forexample, a selected amount of up to the order of 25% of anthracitefines, coke breeze, over oxidized coal and the like.

The headload strength of green briquettes and other preforms can also bemeasurably improved by utilizing a small amount of a water-solublebinder, and of the order of two percent, more or less, of the weight ofthe coal. Such water-soluble binder may comp-rise starchy or farinaceousmaterials, waste sulfite liquor, molasses and the like. While therationale of their function or action is not fully comprehended, it hasbeen found in actual operation that they significantly improve theheadload strength of briquettes or other preforms in which they areincorporated.

It has been found that certain variables quite profoundly affect thecharacter of the binder-coal mix and the physical properties of thebriquettes or other preforms molded from such a mix. It has beenascertained that the moisture content of the coal and the proportion ofbinder to coal are of salient importance in the production of briquetteswhich behave satisfactorily in the subsequent carbonization operation.Similarly, as previously pointed out, the heating rates during thecarbonization operation are of major importance and are intimatelycorrelated with the character and structure of the preformed units.

As a result of extensive investigation of the several variables orfactors which might or could influence the quality of the briquettes, itwas determined that the optimum condition for the fabrication ofbriquettes of the desired characteristics involved in careful control ofa number of conditions.

It was found that the moisture content of the coal to be extruded was ofmajor significance. It was learned that such moisture content should beheld within the range of approximately 5% to 8% and that improvedresults could be achieved by introducing a small amount of an effectivewetting agent that lowers the interfacial tension between the coalparticles and the binder magma.

It was also determined that the relative quantity of the binder in thepermix was a very important factor. It was found that excellentpreforrns could be made by employing a relatively low melting point coaltar pitch -F.M.P.) and using this in the preparation of between about12% and 15% on the weight of the coal.

While the addition temperature of the pitch and the temperature ofmixing are not critical, it has been found from experience that addingthe pitch at a temperature of between about 325 F. and 350 F. andholding the temperature of the mix at between about 180 F. and F. insureexcellent mixing and the production of formed units of consistently highquality.

While the above specific mixing procedure has been found to be veryeffective and is thus recommended, it will be understood that thecomprehensive scope of the invention is not confined to such mixingtechnique.

Although certain recommended procedures have been described, it is to beunderstood that these are given didactically to illustrate theunderlying principles of the invention and not as limiting its usefulscope to the descriptive embodiment.

This application is a continuation-in-part of United States applicationSerial No. 158,125, filed April 26, 1950, now abandoned, and UnitedStates application Serial No. 267,158, filed January 18, 1952, nowPatent No. 2,815,316.

I claim:

1. A process of producing a metallurgical grade coke from swelling coalswhich comprises subjecting such coal to flash oxidation with a gascontaining free oxygen, in particulated and fluidized form, at atemperature within the plastic range of the coal for a controlled briefperiod of time; shock cooling the oxidized particulated coal to atemperature at which oxidation of the coal is inhibited; admixing theoxidized coal with a fluent binder to produce a plastic, formable massof uniform consistency; forming the plastic mass into units of selectedsize and shape; carbonizing the formed units by contacting such unitswith a flowing stream of non-reactive gas characterized by a low partialpressure of the components of the coal which are volatile at suchcarboni'zation tem perature; controlling the rate of heat input fromsuch non-reactive gas to said formed units substantially at the rate ofbetween 25 C. to C. per minute up to substantially 500 C. and thereaftercontrolling such heat input at the rate of from substantially 0.75 C. to125 C. per minute up to the final finishing temperature.

2. A process in accordance with claim 1 in which the binder is comprisedessentially of coal tar pitch.

3. A process in accordance with claim 1 in which the binder is comprisedessentially of coal tar pitch in which is incorporated a wetting agentsubstantive to the coal.

4. A process in accordance with claim 1 in which the binder is compisedessentially of coal tar pitch in which is incorporated an adjuvant whichimparts headload strength to the said formed units.

5. A process in accordance with claim 1 in which a predeterminedpercentage efiective of a carbohydrate binder is incorporated in thecoal tar pitch.

6. A process in accordance with claim 1 in which the headloadstrength-imparting adjuvant is chosen from the group consisting of wastesulfite liquor, amylaceous and saccharogenic coal-binding compounds.

7. A process in accordance with claim 1 in which the oxidizing period inthe plastic range is less than about twenty seconds.

8. A process in accordance with claim 1 in which the binder comprisesessentially a coal tar pitch having a melting point of approximately 130F.

9. A process in accordance with claim 1 in which the binder is coal tarpitch and comprises from approximately 12.5% to 15% of the binder-coalmix.

10. A process in accordance with claim 1 in which the oxidation of thecoal is effected at a temperature above about 500 F.

11. A process in accordance with claim 1 in which the oxidation of thecoal is effected at a temperature of between about 675 F. and 800 F. andwithin a period of less than approximately 15 seconds.

References Cited in the file of this patent UNITED STATES PATENTSRe.21,526 Odell 2. Aug. 6, 1940 1,669,023 Runge May 8, 1928 1,775,323Runge Sept. 9, 1930 1,783,982 Runge Dec. 9, 1930 1,983,943 Odell Dec.11, 1934 1,993,198 Wisner Mar. 5, 1935 2,105,832 Becker Jan. 18, 19382,131,702 Berry Sept. 27, 1938 2,276,362 Wolf Mar. 17, 1942 2,314,641Wolf Mar. 23, 1943 2,336,151 Kruppa Dec. 7, 1943 2,341,861 Fuchs Feb.15, 1944 2,512,076 Singh June 20, 1950 2,594,226 Shea Apr. 22, 19522,661,326 Stillman Dec. 1, 1953 2,815,316 Kruppa et al. Dec. 3, 19572,825,679 Baum Mar. 4, 1958 FOREIGN PATENTS 724,774 Great Britain Feb.23, 1955 OTHER REFERENCES Industrial and Engineering Chemistry, June1949, vol. 4, No. 6, p. 1249.

Application of Low Temperature Carbonization, Chemical EngineeringProgress, vol. 50, No. 1, January 1954, pp. 3 to 7, inclusive.

1. PROCESS OF PORUCING A METALLURGICAL GRADE COKE FROM SWELLING COALSWHICH COMPRISES SUBJECTING SUCH COAL TO FLASH OXIDATION WITH A GASCONTAINING FREE OXYGEN, IN PARTICULATED AND FLUIDIZED FORM, AT ATEMPERATURE WITHIN THE PLASTIC RANGE OF THE COAL FOR A CONTROLLED BRIEFPERIOD OF TIME; SHOCK COOLING THE OXIDIZED PARTICULATED COAL TO ATEMPERATURE AT WHICH OXIDATION OF THE COAL IS INHIBITED; ADMIXING THEOXIDIZED COAL WITH A FLUENT BINDER TO PRODUCE A PLASTIC, FORMABLE MASSOF UNIFORM CONSISTENCY; FORMING THE PLASTIC MASS INTO UNITS OF SELECTEDSIZE AND SHAPE; CARBONIZING THE FORMED UNITS BY CONTACT ING SUCH UNITSWITH A FLOWING STREAM OF NON-REACTIVE GAS CHARACTERIZED BY A LOW PARTIALPRESSURE OF THE COMPONENTS OF THE COAL WHICH ARE VOLATILE AT SUCHCARBONIZATION TEMPERATURE; CONTROLLING THE RATE OF HEAT INPUT FROM SUCHNON-REACTIVE GAS TO SAID FORMED UNITS SUBSTANTIALLY AT THE RATE OFBETWEEN 2.5*C. TO 5*C. PER MINUTE UP TO SUBSTANTIALLY 500*C. ANDTHEREAFTER CONTROLLING SUCH HEAT